Trypaea Australiensis Research Articles

Comparative effects of the large bioturbators, Trypaea australiensis and Heloecius cordiformis, on intertidal sediments of Western Port, Victoria, Australia

The effect of bioturbation by the ghost shrimp Trypaea australiensis and semaphore crab Heloecious cordiformis was compared in sediment-filled tanks in the laboratory. Effect of bioturbator density was also investigated with high- and low-density treatments. It was hypothesised that the two species would influence the sediment profile in different ways owing to their contrasting burrowing and feeding habits. Both species increased porosity of surface sediments relative to control tanks. Crab activity did not alter redox potential, but low densities of shrimp created more oxidising conditions and high densities of shrimp created more reducing conditions than controls. Burial of tracer particles by crabs was restricted to the top 5 cm, whereas shrimp mixed particles to depths of 25 cm. Bioturbator density had little effect on the extent of particle mixing. The presence of both shrimp and crabs increased benthic microalgae in the sediments relative to the controls. Again, crabs had the greatest effect at the sediment surface, whereas shrimp also enhanced concentrations at 25 cm depth. High densities of shrimp had the greatest effect. Overall, shrimp bioturbation influenced deeper sediments than crab bioturbation, but there was no clear density-dependent effect.

Comparison of methods for sampling populations of ghost shrimp, Trypaea australiensis (Decapoda: Thalassinidea: Callianassidae)

Coring and pumping methods, commonly used to determine the abundance and population parameters of burrowing ghost shrimp, were assessed in three widely separated south-eastern Australian estuaries. First, a comparison of two sizes of coring tube (0.04 and 0.07 m 2) revealed no significant differences in catches of the ghost shrimp Trypaea australiensis Dana, nor differences in precision. However, the smaller sized core was consistently more cost effective. Second, when sampling a 0.1 m 2 quadrat, it was found that 12 “pumps” of a suction pump produced significantly higher numbers of individuals at most sites than using either four, eight or 16 pumps. In a third set of experiments, the coring method was compared to the pumping method, in terms of sampling efficiency, abundance estimates and sex ratios of captured ghost shrimp. Pumping was found to be more efficient, catching significantly greater numbers of ghost shrimp per minute than the coring. In addition, pump catches displayed a more normal size distribution than catches from the core and included a wider range of sizes. Sex ratios of catches from coring was 1:1, while catches from pumping were significantly biased toward females (0.71:1). Since female-biased sex ratios are characteristic of many thalassinid populations, this latter result probably reflects actual sex ratios for T. australiensis and not method based size selectivity.

Measurements of oxygen uptake, heart and gill bailer rates of the callianassid burrowing shrimp Trypaea australiensis Dana and its responses to low oxygen tensions

Burrowing shrimps are likely to encounter temporal and spatial changes in oxygen tension as they move about in their burrows. Callianassid shrimps apparently tolerate a wide range of oxygen tensions so the physiological nature of this tolerance is of interest. The oxygen uptake, heart and gill bailer rates of the burrow-dwelling shrimp, Trypaea australiensis Dana were studied in the laboratory, particularly during falling oxygen tension. Trypaea australiensis had a critical point ( P c ) of oxygen uptake of about 5 kPa and showed a very low “settled” or routine respiration rate (25.6 ± 6.31 μmol O 2 · kg −1 · min −1, mean ± sd) for a decapod crustacean of this size (2 to 6 g wet weight). Some of the variation in oxygen uptake rate was explained by body size and the weight exponent ( b) increased significantly when shrimp recovered from handling. The heart and bailers of T. australiensis showed the same general responses to a gradual fall in oxygen tension as do other crustaceans that are strong “oxy-regulators” and the heart beat decreased but persisted during anoxic conditions, and responded rapidly to re-oxygenation. An acute fall in oxygen tension (<1.5 kPa) did not lead to bradycardia. These results are consistent with an animal that attempts to prolong aerobiosis for as long as possible but which nevertheless curtails heart rate and presumably metabolic rate in response to long-term anoxia.